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What is the best combi boiler?

Combi boilers offer one of the most efficient ways to heat your home. Here, we look at the boiler brands currently on the market, what they offer and how much you can buy them for.

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Choosing the perfect combi boiler can be confusing, with so many things to consider, from the size of your house to the location it will be installed.

Like any other household appliance, choosing between the many boiler brands and models available can also be a difficult task. While some provide a more affordable option for those in smaller properties, some promise a longer lifespan backed up by a longer manufacturer warranty.

Here we take a closer look at everything you need to consider.

How much does it cost to install a new boiler?

Getting a new boiler fitted will generally cost anywhere between £1,549 and £3,500, which includes the price of the unit itself, the installation and warranty registration.

There are a wide range of factors to consider when working out the cost of a combi boiler installation. Everything from brand and type, to where in the home it will be installed and even where in the country you live, will all affect the final cost.

The type of boiler you choose will also have a significant bearing on this cost. Combi, system and regular boilers all work differently and provide varying levels of power to the central heating system based on the requirement of a particular property.

How do combi boilers work?

Combination boilers are often smaller and more compact than other central heating systems, as they combine two household functions, heating and hot water, into one appliance – hence the nickname, “Combi”.

Combis heat water directly from the mains when a tap is turned on. There’s no need for a hot water storage cylinder, or a cold-water storage tank, which are requirements in other types of central heating system such as system boilers and regular boilers.  

Combis are the most popular for small to medium sized homes; since they take up a small amount of space and can heat a small amount of water incredibly fast. 

What makes a good combi boiler?

Some of the key things to look out for when comparing combi boiler models are:

Hot Water Flow Rate

This is the speed at which your boiler can heat and supply water to your taps, baths, showers and appliances.

If you have a busy home that regularly has two showers running at the same time, a high flow rate above 13 litres/minute is recommended.

Central Heating Output

This measures how powerful a boiler is and how many radiators it can heat. The higher the kW, the more radiators it can power.

If you have just a few radiators, for example in a small one-bedroom flat, then it’s best to choose a smaller boiler for the greatest levels of economy.

For a three to four-bedroom house with around 10 radiators, a small to medium sized combi between 24 – 30Kw will be more suitable, while those with even bigger properties with as many as 20 radiators may need to go for a 35 – 42 kW appliance. However, at this point it may be more appropriate to look at a system boiler.

Length of Warranty

Depending on what boiler you choose, each comes with a manufacturer backed warranty of varying lengths.

This means that you won’t have to pay for any call outs, boiler repairs or replacement parts for the term of the warranty term. The longer the warranty, the more protection you’ll have should something go wrong with your unit.

However, you’ll need to make sure that you get an annual service in order to keep your warranty valid.

For a smaller property with one bedroom and one bathroom, we offer an Ideal Logic C24 Combi from £1,549, which comes with a free a 2-year warranty, with the option of upgrading to 5 or 10 years.

For those with households that require a more powerful unit, most manufacturer warranties range from 5-10 years. Here at Boiler Plan, all our Veissmann, Vaillant and Worcester Bosch boilers all come with an amazing 10-year warranty.

Boiler Measurements

The measurements of the actual boiler can be an important consideration when planning where you’re going to install it. While this won’t be a problem should you be installing in somewhere like a loft, you may need to be more careful when fitting it into a pre-existing kitchen cupboard, for example.

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How to choose the best combi boiler for your home

Choosing the right combi boiler has a lot to do with how much demand is placed on your heating system as a result of the type of property you live in.

Here we look at some of our best combi options for three different property types and see which rank highest in terms of price, flow rate, central heating output and size.

Combi Boiler - Example 1

Property Type: Semi-Detached

Fuel: Gas

Bathrooms: 1

Bedrooms: 3

Boiler location: Ground Floor

Recommended Combi Boilers:

Best for Price:

Ideal Logic C30 Combi. 30kW

Price: £1,904 inc VAT

Hot water flow rate: 12.4 litres/min

Heating output: 30kW

Size: w.395mm x h.700mm x d.278mm

Warranty: 5 years

The Logic Combi condensing gas boiler is a reliable boiler that has been awarded the Queen's Award for Enterprise and Innovation and comes recommended by the Energy Saving Trust.

Best for flow rate and size:

Baxi Assure 30Kw Combi

Price: £1,959

Hot water flow rate: 15 litres/min

Heating output: 30kW

Size: w.390mm x h.700mm x d.285mm

Warranty: 5 years

The Baxi Assure combi boiler is an efficient and durable choice.  It uses the right amount of fuel to meet the set central heating and water temperatures - saving you money on your fuel bills.

Best for Warranty - Option 1

Vaillant ecoTEC Pro 30 Combi (30kW)

Price: £2,236

Hot water flow rate: 12.3 litres/min

Heating output: 30kW

Size: w.4400mm x h.720mm x d.338mm

Warranty: 10 years

The ecoTEC Pro range combine the built-in quality, reliability and performance you’d expect from Vaillant, with a simple design and approach. This highly efficient boiler has been awarded the Quiet Mark Accreditation.

Best for Warranty - Option 2

Worcester Bosch Greenstar 30i Combi

Price: £2,282

Hot water flow rate: 10.8 litres/min

Heating output: 30kW

Size: w.400mm x h.710mm x d.330mm

Warranty: 10 years

The Worcester Bosch Greenstar 30i is perfect for small to medium-sized homes with one bathroom. This boiler range is well established, award-winning and has been installed in over 1 million homes across the UK.

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Combi Boiler - Example 2

Property Type: Detached House

Fuel: Gas

Bathrooms: 3

Bedrooms: 5

Boiler location: Ground Floor

Recommended Combi Boilers:

Best for price and power

Baxi Assure 36kW

Price: £2,282

Hot water flow rate: 15 litres/min

Heating output: 36kW

Size: w.390mm x h.700mm x d.285mm

Warranty: 5 years

The Baxi Assure 36kW is a good choice for larger properties that need a system with a little more power, both in terms of its hot water flow rate and heating output. It’s also compact enough to fit in a kitchen cupboard and is whisper quiet when operating.

Best for Warranty - Option 1

Worcester Bosch Greenstar 8000 35Kw Life Combi

Hot water flow rate: 12.5 litres/min

Heating output: 35kW

Size: w.440mm x h.770mm x d.365mm

Warranty: 10 years

The new Greenstar Life is Worcester Bosch's most powerful wall hung combi yet and builds upon the award-winning Greenstar CDi Classic by adding new features and a modern new design. Its round control panel boasts easier to use push buttons to improve heating and hot water control.

Best for Warranty - Option 2

Vaillant ecoTec Plus 835 Combi

Hot water flow rate: 14.3 litres/min

Heating output: 35kW

Size: w.440mm x h.720mm x d.372mm

Warranty: 10 years

The Vaillant ecoTEC plus range combines fantastic efficiency, high performance and great usability. Thanks to continuous modulation and real combustion control by a multi-sensor system, they achieve high efficiency at the lowest emissions.

However, if having a larger house also means that there are higher demands placed on your central heating, such as regularly needing two showers to be used at the same time, it may prove more efficient to look at other system types. For example, system and regular boilers are often a better choice in these cases as they provide the extra water required through a back-up supply.

System boilers are economical to run and use a hot water cylinder to store and deliver the extra hot water requirement to multiple taps. Regular Boilers use both a cold-water storage tank and a hot water cylinder and are ideal for large homes with 3 or more bathrooms or even properties in low water pressure areas.

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Combi Boiler - Example 3

Property Type: Flat

Fuel: Gas

Bathrooms: 1

Bedrooms: 1

Boiler Location: Ground Floor

Recommended Combi Boiler:

Ideal Logic C24 Combi

Price: £1,549

Hot water flow rate: 9.9 litres/min

Heating Output: 24Kw

Size: w.395mm x h.700mm x d.278mm

Warranty: 2 years

This boiler is perfectly suited to one-bed flats and will provide all the heating and hot water required by this type of property.

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What are the best combi boiler brands?

At Boiler Plan, we only instal boilers that we trust and that we know can be relied upon to provide heat and hot water to your home when you need it.

These range from more affordable models from brands such as Ideal, to more premium ones from brands like Worcester Bosch and Veissmann.

Worcester Bosch

Worcester Bosch is the market leading boiler brand in the UK, with an enviable product range that also includes hot water cylinders, renewable technologies, heat pumps and solar water heating systems.

But it’s the brand’s range of combi boilers that has helped it become a firm favourite as well as receive plaudits within the industry, with its Greenstar gas range having been awarded a Which? Best buy accreditation 11 years in a row.


While German brand Veissmann has expanded to take in everything from investments to large scale industrial solutions, it’s heating systems that remain at the heart of the business.

Its best-selling Vitodens condensing boiler range combines efficiency with superior performance and reliability.

As well as being user friendly, the range has been designed with smart technology in mind to help you save money and take control of your heating.


British brand Baxi has a long history of heating manufacture that dates all the way back to 1866.

With a focus on simplicity, its range are easy to use and straightforward to install, maintain and service.

As well as its award-winning combi range, Baxi is also at the forefront of new heating technology and is developing and testing its own hydrogen boiler.


International family-owned company Vaillant has been manufacturing heating solutions for more than 140 years, creating products that have helped to revolutionise the industry, from water heaters in the early 1900’s to helping to pioneer the combi boiler over 35 years ago.

All of its products feature high efficiency ratings and low emissions, and come with an enviable reputation for performance, quality and reliability.


Founded in 1906, Ideal were responsible for one of the first British boilers, the Ideal Cookanheat, which combined an open fire, central heating boiler, cooking oven and hot cupboard, all in one unit.

Today it provides combi boilers for a range of budgets and all delivering high levels of efficiency and reliability, with its Ideal Logic C30 and Ideal Vogue 32c combi among its most popular models.

Which brand should you pick?

 Like any product, the manufacturer brand of your combi boiler will have a bearing on how much you’ll pay for it. While some brands provide more affordable options, particularly for those living in smaller properties, more premium brands ensure a longer life product that will usually be backed up by 10-year warranty.

However, brand isn’t the only thing you’ll need to consider, as our ‘How Much Does a New Boiler Cost’ guide illustrates. Here, we provide a full breakdown of everything you need to consider when shopping for a new combi.

How can I pay for my boiler?

For those unfortunate enough to be faced with a broken combi boiler, there’s no need to panic as there are a number of payment options available to help you pay for a new one.

At Boiler, we offer a range of payments plans, including interest-free, Buy Now Pay Later and 6.9% APR Representative options - ranging from 12 to 120 months. Of course, you can always opt for a straightforward cash purchase, which is payable on installation.

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